It is not something that you "HAVE" to have. It is just a very useful tool to monitor and market your site as Google sees it.

My suggestion to you is to open the account as HTMLBasicTutor suggested. The do the following:

1) Find Configuration>settings and set your preferred domain.
2) Find Optimization>Sitemaps and submit your sitemap.
3) Find Health>Blocked URLs and make sure your robots.txt is working the way you want it.
4) Find Home>Preferences and forward messages to your email address.
5) I would also suggest linking you Webmaster tools account to your Google Analytics account (if you use one)

Once you do that, wait a few weeks, and just surf all of the options. Do this periodically. Pay close attention to the messages, HTML improvements, alerts, errors, etc. Make sure you don't have any crawl errors, and if you do, fix them. Make sure your site is being indexed. Make sure your are getting more links to your site. Look through your keywords to uncover marketing opportunities, etc.

Once you start getting more into SEO and marketing of your site, these tools will become invaluable. Same goes for Bing webmaster tools. They are more or less the same thing. Hope that helps.